To reduce transmitter's range......


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jacob

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#1
hi techies,

i want to reduce the range of a radio transmitter do i just simply reduce the length of the antenna? can i replace the antenna with just a piece of common wire? thanks for any help.
 

Jul 23, 2005
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#2
hi techies,

i want to reduce the range of a radio transmitter do i just simply reduce the length of the antenna? can i replace the antenna with just a piece of common wire? thanks for any help.
antenna length corresponds to wavelength.
reduce antenna length hence will not change transmitter range.

the medium (air) plays a big part to attenuate the signal and affects transmitting range.

In labs, they put electrical shield (e.g. grounded mesh cage) at the boundry where you want the transmission to stop. Of course this is not easy at home.

I put my BB Box in bedroom and for sure the signal is weak in the sitting room, since there is no direct unblocked path between box and sitting room.
 

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LittleWolf

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#5
hi techies,

i want to reduce the range of a radio transmitter do i just simply reduce the length of the antenna? can i replace the antenna with just a piece of common wire? thanks for any help.
You can possibly reduce the range. You can also possibly cause damage to the transmitter. You could also possibly cause radio interference since a changed antenna can radiate harmonics and parasitics that you may not even be aware of much more efficiently than the designated antenna.

If you don't know what you're doing, don't do it. Note that many license-free RF devices are only approved for use in unmodified form; modifying them could get you into legal trouble.
 

LittleWolf

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#7
a video and audio transmission set.

my set max range is 100ft. i wanted to reduce it by half.
If you have a removable antenna, you can insert a 6dB attenuator between the transmitter and the antenna. This assumes you're talking about free space propagation. For indoors, builtup, or otherwise obstructed environments it is extremely difficult to predict the range.
 

zcf

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Apr 10, 2005
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#8
just cover the antenna with different thickness of materials, then choose the one you want? :think:
 

jacob

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#9
If you have a removable antenna, you can insert a 6dB attenuator between the transmitter and the antenna. This assumes you're talking about free space propagation. For indoors, builtup, or otherwise obstructed environments it is extremely difficult to predict the range.
sounds like a good solution. 6dB attenuator cuts the range by half right? can get it in simlim tower? any idea what's the typical cost?
 

CYRN

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#11
sounds like a good solution. 6dB attenuator cuts the range by half right? can get it in simlim tower? any idea what's the typical cost?
6db cuts the transmission power by half... but it does not mean range is reduced proportionally.

note the attenuating frequency.

Littlewolf is rite in highlighting the diff between spec range and real world performance.
 

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Gengh

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#12
6db cuts the transmission power by half... but it does not mean range is reduced proportionally.

note the attenuating frequency.

Littlewolf is rite in highlighting the diff between spec range and real world performance.
6dB cuts power down to 1/4. Effective range in a completely open environment is halved as power is inversely proportional to the square of the distance. But yah, in real world situations, things can be very different.

Price depends on the type of connector and frequency of interest, you can get an idea here: http://singapore.rs-online.com/web/search/searchBrowseAction.html?method=retrieveTfg&binCount=50&Ne=4294960157&Ntt=attenuator&Ntk=I18NAll&Nr=AND(avl%3asg%2csearchDiscon_sg%3aN)&Ntx=mode%2bmatchallpartial&N=4294857545&Nty=1 and here: http://sg.farnell.com/jsp/search/browse.jsp?N=500006+1004508&Ntk=gensearch_001&Ntt=attenuator&Ntx=. I'm sure you can find them for cheaper in Sim Lim Tower though.
 

CYRN

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#13
oops... paiseh...:embrass:

forgetting wat I learned liao... 3db then is half power rite?

heeheehee
 

lsisaxon

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Nov 29, 2004
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#14
hi techies,

i want to reduce the range of a radio transmitter do i just simply reduce the length of the antenna? can i replace the antenna with just a piece of common wire? thanks for any help.
Yes you can. You'll just be making it work less efficiently. But do note what LittleWolf mentioned that it might cause harmonics problems.
 

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lsisaxon

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Nov 29, 2004
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#15
6db cuts the transmission power by half... but it does not mean range is reduced proportionally.

note the attenuating frequency.

Littlewolf is rite in highlighting the diff between spec range and real world performance.
For power, it's 3dB.
 

lsisaxon

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Nov 29, 2004
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#16
a video and audio transmission set.

my set max range is 100ft. i wanted to reduce it by half.
Why would you want to do that? The range is determined by 1) the radiated power, as well as 2) the sensitivity of the receiver.
 

LittleWolf

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Jan 23, 2005
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#17
Why would you want to do that?
Beyond privacy reasons, it is only courteous (and good, in some cases mandatory practice) to use minimum necessary power (and thereby reduce interference/RF pollution). Same reason why one should adjust the volume of one's radio/TV set to a level where the neighbours are not forced to listen to it ...
 

Gengh

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#18
Beyond privacy reasons, it is only courteous (and good, in some cases mandatory practice) to use minimum necessary power (and thereby reduce interference/RF pollution). Same reason why one should adjust the volume of one's radio/TV set to a level where the neighbours are not forced to listen to it ...
Ideally a transmitter and receiver should work in tandem and automatically determine the power to radiate. But I don't think such a feature would be common in mass market consumer devices... So they would just transmit at full power to ensure maximum coverage.

But I guess the 802.11n standard allows for some level of directionality, not sure if this is something that's properly exploited to minimise the spread of the signal.
 

jacob

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#19
Beyond privacy reasons, it is only courteous (and good, in some cases mandatory practice) to use minimum necessary power (and thereby reduce interference/RF pollution). Same reason why one should adjust the volume of one's radio/TV set to a level where the neighbours are not forced to listen to it ...
that's right. that's the reason to reduce the range.
 

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